A method of manufacturing an integrated circuit utilizes solid phase epitaxy to form an elevated source region and an elevated drain region. The method includes providing an amorphous semiconductor material and crystallizing the amorphous semiconductor material without damaging a high-k gate dielectric...http://www.google.com/patents/US6403434?utm_source=gb-gplus-sharePatent US6403434 - Process for manufacturing MOS transistors having elevated source and drain regions and a high-k gate dielectric

A method of manufacturing an integrated circuit utilizes solid phase epitaxy to form an elevated source region and an elevated drain region. The method includes providing an amorphous semiconductor material and crystallizing the amorphous semiconductor material without damaging a high-k gate dielectric layer. The semiconductor material can be silicided. A shallow source drain implant can also be provide.

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Claims(20)

What is claimed is:

1. A method of manufacturing an integrated circuit, the integrated circuit including a gate structure on a substrate, the substrate including a shallow source extension and a shallow drain extension, the gate structure including a gate conductor above a high-k gate dielectric, the method comprising steps of:

providing the gate structure on the substrate;

forming a shallow amorphous region in the substrate;

providing spacers on sidewalls of the gate structure;

etching the substrate to remove at least a portion of the shallow amorphous region;

providing an amorphous semiconductor layer above the substrate and over the gate structure;

removing a portion of the amorphous semiconductor layer to expose the gate structure; and

forming a single crystalline semiconductor material from the amorphous semiconductor layer and a remaining portion of the shallow amorphous region via an annealing process.

2. The method of claim 1, further comprising:

before the providing spacers step, doping the shallow amorphous region.

3. The method of claim 1, further comprising:

after the second forming step, siliciding the single crystalline material at a source location and at a drain location, the single crystalline material being silicided at a location above an original top surface of the substrate.

4. The method of claim 3, wherein the siliciding step is a nickel silicide process performed at a temperature of less than 500° C.

5. The method of claim 1, wherein the gate structure includes a cap layer.

6. The method of claim 1, wherein the second forming step includes an excimer laser annealing step.

7. The method of claim 1, wherein the amorphous semiconductor layer includes silicon.

8. The method of claim 1, wherein the substrate includes single crystalline silicon.

The present application relates to integrated circuits (ICs) and methods of manufacturing integrated circuits. More particularly, the present application relates to a method of manufacturing integrated circuits having transistors with elevated source and drain regions and high-k gate dielectrics.

Currently, deep-submicron complementary metal oxide semiconductor (CMOS) is the primary technology for ultra-large scale integrated (ULSI) devices. Over the last two decades, reducing the size of CMOS transistors and increasing transistor density on ICs has been a principal focus of the microelectronics industry. An ultra-large scale integrated circuit can include over 1 million transistors.

The ULSI circuit can include CMOS field effect transistors (FETS) which have semiconductor gates disposed between drain and source regions. The drain and source regions are typically heavily doped with a P-type dopant (boron) or an N-type dopant (phosphorous).

The drain and source regions generally include a thin extension (shallow source and drain extensions) that is disposed partially underneath the gate to enhance the transistor performance. Shallow source and drain extensions help to achieve immunity to short-channel effects which degrade transistor performance for both N-channel and P-channel transistors. Short-channel effects can cause threshold voltage roll-off and drain-induced barrier-lowering. Shallow source and drain extensions and, hence, controlling short-channel effects, are particularly important as transistors become smaller.

Conventional techniques utilize a double implant process to form shallow source and drain extensions. According to the conventional process, the source and drain extensions are formed by providing a transistor gate structure without sidewall spacers on a top surface of a silicon substrate. The silicon substrate is doped on both sides of the gate structure via a conventional doping process, such as, a diffusion process or an ion implantation process. Without the sidewall spacers, the doping process introduces dopants into a thin region just below the top surface of the substrate to form the drain and source extensions as well as to partially form the drain and source regions.

After the drain and source extensions are formed, silicon dioxide spacers, which abut lateral sides of the gate structure, are provided over the source and drain extensions. With the silicon dioxide spacers in place, the substrate is doped a second time to form deep source and drain regions. During formation of the deep source and drain regions, further doping of the source and drain extensions is inhibited due to the blocking capability of the silicon dioxide spacers.

As the size of transistors disposed on ICs decreases, transistors with shallow and ultra-shallow source/drain extensions become more difficult to manufacture. For example, a small transistor may require ultra-shallow source and drain extensions with a junction depth of less than 30 nanometer (nm). Forming source and drain extensions with junction depths of less than 30 nm is very difficult using conventional fabrication techniques. Conventional ion implantation techniques have difficulty maintaining shallow source and drain extensions because point defects generated in the bulk semiconductor substrate during ion implantation can cause the dopant to more easily diffuse (transient enhanced diffusion, TED). The diffusion often extends the source and drain extension vertically downward into the bulk semiconductor substrate. Also, conventional ion implantation and diffusion-doping techniques make transistors on the IC susceptible to short-channel effects, which result in a dopant profile tail distribution that extends deep into the substrate.

The source region and drain regions can be raised by selective silicon (Si) epitaxy to make connections to source and drain contacts less difficult. The raised source and drain regions provide additional material for contact silicidation processes and reduce deep source/drain junction resistance and source/drain series resistance. However, the epitaxy process that forms the raised source and drain regions generally requires high temperatures exceeding 1000° C. (e.g., 1100-1200° C.). These high temperatures increase the thermal budget of the process and can adversely affect the formation of steep retrograde well regions and ultra shallow source/drain extensions.

The high temperatures, often referred to as a high thermal budget, can produce significant thermal diffusion which can cause shorts between the source and drain region (between the source/drain extensions). The potential for shorting between the source and drain region increases as gate lengths decrease.

In addition, high temperature processes over 750 to 800° C. can cause dielectric materials with a high dielectric constant (k) to react with the substrate (e.g., silicon). High-k (k>8) gate dielectrics are desirable as critical transistor dimensions continue to decrease. The reduction of critical dimensions requires that the thickness of the gate oxide also be reduced. A major drawback to the decreased gate oxide thickness (e.g., <30 Å) is that direct tunneling gate leakage current increases as gate oxide thickness decreases. To suppress gate leakage current, material with a high dielectric constant (k) can be used as a gate dielectric instead of the conventional gate oxides, such as thermally grown silicon dioxide.

High-k gate dielectric materials have advantages over conventional gate oxides. A high-k gate dielectric material with the same effective electrical thickness (same capacitive effect) as a thermal oxide is much thicker physically than the conventional oxide. Being thicker physically, the high-k dielectric gate insulator is less susceptible to direct tunnel leakage current. Tunnel leakage current is exponentially proportional to the gate dielectric thickness. Thus, using a high-k dielectric gate insulator significantly reduces the direct tunneling current flow through the gate insulator.

High-k materials include, for example, aluminum oxide (Al2O3), titanium dioxide (TiO2), and tantalum pentaoxide (TaO5). Aluminum oxide has a dielectric constant (k) equal to eight (8) and is relatively easy to make as a gate insulator for a very small transistor. Small transistors often have a physical gate length of less than 80 nm.

Thus, there is a need for an integrated circuit or electronic device that includes transistors not susceptible to shorts caused by dopant thermal diffusion. Further still, there is a need for transistors with elevated source and drain regions manufactured in an optimized annealing process. Even further still, there is a need for elevated source and drain regions which are formed in a low thermal budget (low temperature) process. Yet further, there is a need for a transistor with elevated source and drain regions and a high-k gate dielectric. Yet even further, there is a need for a process of forming a transistor with elevated source and drain regions and a high-k gate dielectric in a low thermal budget process.

SUMMARY OF THE INVENTION

An exemplary embodiment relates to a method of manufacturing an integrated circuit. The integrated circuit includes a gate structure on a substrate. The substrate includes a shallow source extension and a shallow drain extension. The gate structure includes a gate conductor above a high-k gate dielectric. The method includes steps of: providing the gate structure on the substrate, forming a shallow amorphous region in the substrate, providing spacers on sidewalls of the gate structure, and etching the substrate to remove at least a portion of the shallow amorphous region. The method also includes steps of: providing an amorphous semiconductor layer above the substrate and over the gate structure, removing a portion of the amorphous semiconductor material to expose the gate structure, and forming a single crystalline semiconductor material from the amorphous semiconductor material and a remaining portion of the shallow amorphous region via a laser annealing process.

Another exemplary embodiment relates to a method of manufacturing an ultra-large scale integrated circuit including a transistor. The method includes providing a gate structure on a top surface of a substrate, providing a pair of spacers for the gate structure, depositing an amorphous semiconductor material above the top surface of the substrate, removing the amorphous semiconductor material to a level below a bottom surface of the cap layer, and crystallizing the amorphous semiconductor material. The gate structure includes a gate conductor and a cap layer. The amorphous semiconductor material is crystallized in an annealing process. The annealing process is prevented from overheating a high-k gate dielectric within the gate structure.

Yet another exemplary embodiment relates to a process of forming a transistor with elevated source and drain regions. The process includes providing a gate structure, providing an amorphization implant to a substrate, providing a spacer structure to the gate structure, depositing an amorphous semiconductor material above the substrate and the gate structure, and crystallizing the amorphous semiconductor material to form single crystalline material. The gate structure includes a high-k gate dielectric above the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments will hereafter be described with reference to the accompanying drawings, wherein like numerals denote like elements, and:

FIG. 1 is a cross-sectional view of a portion of an integrated circuit in accordance with an exemplary embodiment of the present invention, the integrated circuit including a transistor with elevated source and drain regions and a high-k gate dielectric;

FIG. 2 is a cross-sectional view of the portion of the integrated circuit illustrated in FIG. 1, showing a gate stack formation step, a shallow amorphization implant step, and a shallow source and drain extension dopant implant step;

FIG. 3 is a cross-sectional view of the portion of the integrated circuit illustrated in FIG. 2, showing a spacer structure formation step;

FIG. 4 is a cross-sectional view of the portion of the integrated circuit illustrated in FIG. 3, showing an anisotropic etching step;

FIG. 5 is a cross-sectional view of the portion of the integrated circuit illustrated in FIG. 4, showing an amorphous semiconductor deposition step;

FIG. 6 is a cross-sectional view of the portion of the integrated circuit illustrated in FIG. 1, showing a chemical mechanical polish (CMP) step and a laser annealing step; and

FIG. 7 is a cross-sectional view of the portion of the integrated circuit illustrated in FIG. 1, showing a chemical etching step and a siliciding step.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIG. 1, a portion 10 of an integrated circuit (IC) includes a transistor 12 which is disposed on a semiconductor substrate 14, such as, a wafer. Semiconductor substrate 14 is preferably a bulk P-type silicon substrate. Alternatively, substrate 14 can be any type of IC substrate including a gallium arsenide (GaAs), germanium, or a semiconductor-on-insulator (SOI) substrate (e.g., a silicon-on-glass substrate).

Transistor 12 can be a P-channel or N-channel metal oxide semiconductor field effect transistor (MOSFET) and is described below as an N-channel transistor. Transistor 12 includes a gate structure 18, an elevated source region 22, and an elevated drain region 24. Regions 22 and 24 extend from a top surface 21 (above a top surface 27 of substrate 14) to a bottom 55 in substrate 14. Regions 22 and 24 are 200-1000 Å deep (from surface 21 to bottom 55) and include a source extension 23, a drain extension 25, a deep source region 33, and a deep drain region 35. For an N-channel transistor, regions 22 and 24 are heavily doped with N-type dopants (e.g., 5×1019-1×1020 dopants per cubic centimeter). For a P-channel transistor, regions 22 and 24 are heavily doped with P-type dopants (5×1019-1×1020 dopants per cubic centimeter).

Extensions 23 and 25 are preferably ultra-shallow extensions (e.g., junction depth is less than 20 nanometers (nm), 100-250 Å), which are thinner than regions 33 and 35. Extensions 23 and 25 are connected to regions 33 and 35, respectively, and are disposed partially underneath gate structure 18. Regions 33 and 35 are preferably more than 100 Å thick (e.g. 150 to 300 Å) from surface 21 to surface 27.

A channel region 41 underneath gate structure 18 separates extensions 23 and 25. Region 41 can be doped according to device parameters. For example, region 41 can be doped according to a super steep retrograded well region.

Ultra-shallow extensions 23 and 25 help transistor 12 achieve substantial immunity to short-channel effects. Short-channel effects can degrade the performance of transistor 12 as well as the manufacturability of the IC associated with transistor 12. Regions 22 and 24 and extensions 23 and 25 have a concentration of 1019 to 1020 dopants per cubic centimeter. An appropriate dopant for a P-channel transistor is boron, boron diflouride, or iridium, and an appropriate dopant for an N-type transistor is arsenic, phosphorous, or antimony.

Layer 34 is preferably conformally deposited in a metal organic CVD process after any necessary high temperature annealing steps to prevent crystallization of amorphous Ta2O5 material. Alternatively, layer 34 can be formed according to the process of U.S. Pat. No. 6,100,120.

After dielectric layer 34 is deposited, a 30-40 nm thick layer of gate conductor 36 is deposited above dielectric layer 34 in a low temperature process by CVD. Gate conductor 36 is preferably a metal, such as TiN. Alternatively, conductor 36 can be polysilicon or polysilicon/germanium.

Conductor 36 is preferably deposited by chemical vapor deposition (CVD) or sputter deposition and selectively etched by plasma dry etching to form the particular structure for transistor 12. Gate structure 18 has a height or thickness of 500-2000 Å.

A silicide layer 56 is deposited or sputtered on top of source region 22 and drain region 24. Preferably, layer 56 is a nickel silicide (WSix). Alternatively, layer 56 can be any type of refractory metal and silicon combination, such as, a cobalt silicide, tungsten silicide, or other silicide material. Preferably, layer 56 is 150-300 Å thick. Metal contacts 68 can be coupled to layer 56 through insulating layer 48 to connect regions 22 and 24 to conductive lines 70.

Transistor 12 can be an N-channel or a P-channel field effect transistor, such as, a metal oxide semiconductor field effect transistor (MOSFET). Transistor 12 is at least partially covered by insulative layer 48 and is preferably part of an ultra-large scale integrated (ULSI) circuit that includes one million or more transistors.

With reference to FIGS. 1-7, the fabrication of transistor 12, including high-k gate dielectric layer 34, elevated source region 22 and elevated drain region 24, is described as follows. The advantageous process allows deep source and drain regions 33 and 35 to be formed with appropriate dopant activation without adversely affecting layer 34. The process also reduces the lateral spread of dopants into channel 41 and thereby reduces susceptibility to short circuits between extensions 23 and 25.

With reference to FIG. 2, transistor 12 includes a gate stack or gate structure 18 including a cap layer 80, a gate conductor 36 and a gate dielectric layer 34. Preferably, gate dielectric layer 34 is deposited or formed on top of surface 27 and conductor 36 is deposited or formed over layer 34. Cap layer 80 is deposited on top of gate conductor 36 by CVD. Layer 80, conductor 36 and layer 34 are selectively etched to leave gate structure 18 on a top surface 27 of substrate 14. Preferably, conductor 36 is 500 to 2000 Å thick above a 10 to 60 Å thick layer 34. Layer 80 is preferably a 150 to 300 Å thick layer of silicon nitride (Si3N4). Alternatively, layer 80 can be other materials.

After gate structure 18 is formed, substrate 14 is subject to a shallow amorphization implant to form an amorphization or amorphous region 40. Amorphous region 40 can be created by subjecting substrate 14 to an ion implantation technique. Ion implantation can be performed by implantation devices manufactured by companies, such as, Verion Company of Palo Alto, California, Genius Company, and Applied Materials, Inc. Region 40 is preferably a shallow or thin amorphous region or layer of substrate 14 (e.g., a depth between 100 and 500 Å). The implantation technique can charge semiconductor ions, preferably, electrically neutral species (such as, silicon, germanium, or xenon ions) to approximately 10-100 kilo-electron volts (keVs) and implant them into substrate 14. The silicon, germanium or xenon ions change the single crystal silicon associated with substrate 14 into amorphous silicon at region 40. Region 40 corresponds to source and drain regions 22 and 24.

After region 40 is formed, substrate 14 is subjected to a follow-up dopant implant (a shallow source drain extension dopant implant). Preferably, N-type or P-type dopants are provided by ion implantation to a depth of 100-250 Å below surface 27. The dopants can be implanted in a conventional ion implantation technique (e.g., as ions at 500-1000 keV at a dose of 2×1014-1×1015 dopants per square centimeter). The source drain extension dopant implant is for the formation of extensions 23 and 25 (FIG. 1) in substrate 14.

In FIG. 3, portion 10 is subjected to a spacer formation process which creates spacers 62 on sidewalls 90 of gate structure 18. Preferably, spacers 62 are narrow and are formed in a low temperature process (less than 400° C. to avoid recrystallization of region 40). Spacers 62 are preferably 50-200 Å wide (e.g., left to right) and 500-2000 Å thick (e.g., top (from a top surface of layer 80) to bottom (to top surface 37)). Spacers 62 are formed in a conventional deposition and etch-back process.

In FIG. 4, after spacers 62 are formed, substrate 14 is subjected to an etching or removal process to remove portions of region 40. Preferably, the removal process lowers a top surface of substrate 14 from its original top surface 27. The etching technique can be a plasma dry etching technique in the location of regions 22 and 24 (deep regions 33 and 35) (FIG. 1) which removes 200 to 400 Å of material from substrate 14. Cap layer 80 and spacers 62 protect layer 34 during this anisotropic etching process.

In FIG. 5, after gate structure 18 is formed including spacers 62 and substrate 14 is etched, portion 10 is subjected to a deposition process which provides an amorphous semiconductor layer 53 above substrate 14. Layer 53 is preferably a 2000-5000 Å thick film of the same material as substrate 14 (e.g., silicon). Alternatively, layer 53 can be or include other semiconductor materials such as germanium. Layer 53 can be deposited by low pressure, chemical vapor deposition (LPCVD) at temperatures of less than 450° C. (400-450° C.). Layer 53 corresponds to portions of regions 33 and 35 above top surface 27 of substrate 14 (See FIG. 1).

After layer 53 is deposited, an amorphous material border 85 is located between layer 53 and substrate 14. Border 85 includes the portion of region 40 that remains after the etching of substrate 14 described with reference to FIG. 4. The remaining portion of region 40 corresponds to shallow source and drain extensions 23 and 25 discussed below with reference to FIG. 1.

In FIG. 6, after layer 53 is provided over substrate 14, layer 53 is subject to a planarization process, such as, a chemical mechanical polish (CMP). The CMP step removes layer 53 to expose cap layer 80 above gate conductor 36 in structure 18. After the CMP step to expose layer 80, an overetch technique can further lower layer 53 without lowering layer 80. Preferably, layer 53 is overetched so that a surface 72 of layer 53 is lower than a surface 74 of gate conductor 36. The overetch can be part of the same CMP process used to expose layer 53 or can be a dry or wet etch process. A top surface 76 of cap layer 80 is preferably 300-500 Å above surface 72. The overetching step prevents bridging during subsequent silicidation steps described below with reference to FIG. 7.

In FIG. 6, after overetching, layer 53 is subjected to an annealing process. The annealing process changes the structure of layer 53 from an amorphous state to a single crystalline state (e.g., melts layer 53 which subsequently recrystallizes). Substrate 14 below border 85 acts as a seed layer for layer 53. Preferably, a laser technique is utilized to crystallize layer 53.

In one embodiment, the annealing process is an excimer laser process (e.g., 308 nanometer wavelength) for a pulse duration of approximately 1-20 ns. The annealing technique using an excimer laser can raise the temperature of layer 53 to the melting temperature of layer 53 (1100° C. for silicon). The melting temperature of layer 53 in the amorphous state is significantly lower than that of substrate 14 which is in a crystalline state. For example, the melting temperature of amorphous silicon is 1100° C. and the melting temperature of a single crystalline silicon substrate (C—Si) is 1400° C. Preferably, the annealing process is controlled so that layer 53 is fully melted and substrate 14 is not melted. After the energy associated with the annealing process is removed, layer 53 is recrystallized as a single crystalline material.

The melting associated with the annealing step allows dopants in layer 53 and the remaining portions of region 40 to become activated during the recrystallization. Regions 40 are melted and recrystallized during the annealing step. Preferably, the annealing step utilizes an excimer laser beam to selectively heat locations associated with regions 22 and 24 without significantly heating layer 34. Further, cap layer 80 provides protection on top of metal gate conductor 36 so that layer 34 remains cool during laser exposure. The laser annealing is prevented from overheating layer 34.

Layer 56 is preferably 150-300 Å thick and approximately 30-50 percent of its thickness consumes layer 53. With reference to FIG. 1, after layer 56 is formed, layer 48 is deposited in accordance with a tetraethylorthosilicate (TEOS) process. Preferably, layer 48 is 5000-15000 Å thick. After layer 48 is deposited, conventional MOSFET fabrication processes can be utilized to form contacts 68, lines 70, vias, interconnects, and other devices necessary for portion 10 of the integrated circuit.

It is understood that while the detailed drawings, specific examples, material types, thicknesses, dimensions, and particular values given provide a preferred exemplary embodiment of the present invention, the preferred exemplary embodiment is for the purpose of illustration only. The method and apparatus of the invention is not limited to the precise details and conditions disclosed. For example, although specific types of structures are shown, other structures can be utilized. Various changes may be made to the details disclosed without departing from the scope of the invention which is defined by the following claims.